Many techniques exist for delivering drugs or other medicaments to body tissue. These techniques include oral administration; injection directly into body tissue, such as through an intramuscular injection; topical or transcutaneous administration where the drug is passively absorbed into, or caused to pass across, the skin or other surface tissue; and intravenous administration, which involves introducing a selected drug directly into the blood stream.
Except for topical or transcutaneous administration, the above drug delivery systems tend to be systemic. In other words, administration of the drug is delivered throughout the body by the blood stream. Transcutaneous drug delivery systems deliver a drug locally to a selected area, and are limited to external application of a drug through the patient's skin or other surface tissue. Thus, the above described drug delivery systems generally are not appropriate for the localized treatment of internal body tissue.
Although many medical situations are satisfactorily treated by the general systemic administration of a drug, there are many treatments that are facilitated and/or improved by the ability to deliver or administer a drug locally to a selected portion of internal body tissue, without appreciably affecting the surrounding tissue. One example is the prostate gland, which is subject to various diseases such as prostatitis, benign prostatic hyperplasia, and prostate cancer. The urethra allows relatively easy access to the prostate from outside the patient by means of a catheter.
The urethra includes the prostatic urethra and the membranous urethra. All of the major ducts of the prostate gland open on the surface of the prostatic urethra. These ducts extend into the prostate and branch into ductules (smaller ducts) and eventually end in acini (rounded sacs). The outside of the prostate gland is surrounded by a tough fibrous capsule that serves as a substantial physical barrier between the spongy prostatic tissue and the rest of the peritoneal environment. By using an appropriately designed catheter that is introduced through the urethra, it is possible to access the prostate via the prostatic ducts that extend deep into the gland.
Two previous patents have disclosed catheters for delivering drugs to tissue to the prostate gland via the prostatic urethra and the prostatic ducts. U.S. Pat. Nos. 5,007,897 and 4,423,725 disclose catheters having drug-delivery bladders made from a porous membrane. These patents teach placing the drug-delivery balloon into the prostatic urethra and inflating the balloon with a drug in a fluid form. The drug is pressurize,d so that it is caused to pass through the porous or perforated membrane and transported into the prostatic ducts.
There is a significant problem that results from delivering the drug through this type of membranous balloon. Specifically, the transport of the drug into the prostate gland is impeded and thus much less efficient.
There are two impediments. The first impediment is that the pressurized balloon expands and exerts a force against the walls of the prostatic urethra. This force compresses the prostatic tissue and causes the ducts to restrict and block the flow of the drug into the prostate gland. As a result, the drug typically does not distribute evenly throughout the ducts, nor throughout the prostate gland. Compression of the prostatic ducts also prevents or slows the flow of the drug solution into the interior of the prostate gland.
The second impediment is the porous membrane through which the drug solution must pass before it enters the prostatic ducts. Such an impediment slows the flow of the drug solution and results in additional inefficiency.
Slowing the flow of the drug solution results in longer delivery times and most likely lower levels of drug in the prostate gland. Additionally, a longer administration period requires additional time from the medical personnel. This expense is passed on to the patient, thereby increasing the cost of treatment.
Therefore, there is a need for a catheter that is capable of delivering drugs and diagnostic fluids to the prostate gland via the prostatic urethra and prostatic ducts, wherein the catheter does not compromise flow through the prostatic ducts by exerting pressure against the walls of the prostatic urethra.